This invention relates to a method of sealing a tubular receptacle having a removable lid and containing a material, such as a sample of a biological material to be frozen.
When samples of biological materials contained in receptacles of the above-mentioned type are frozen to very low temperatures, e.g., by immersion of the receptacles into liquid nitrogen, a partial vacuum is created within the receptacles. This vacuum may cause liquid or gas, e.g., nitrogen, to leak into the receptacle, because the removable lid ordinarily does not fit sufficiently tight to the receptacle to prevent such leakage.
During thawing, the gas which has leaked into the receptacle tends to boil instantaneously, and this may cause the lid to be blown off or the receptacle to explode, with the result that the environment is contaminated with the sample and/or that the sample is lost. Therefore, it is essential that receptacles for low temperature storage can be sealed effectively.
It has been proposed to improve the sealing of receptacles for materials to be frozen by providing a gasket of silicon rubber in the zone in which the lid is attached to the receptacle. This proposal has not been successful because the silicon rubber gaskets become rigid and lose flexibility at the low temperatures, viz. down to -196.degree. C., which occur when liquid nitrogen is used as freezing medium.
The object of the invention is to seal a receptacle of the above-mentioned type in a manner such that liquid or gas does not enter the receptacle during the freezing operation.
Another object is to provide a sealing method which can be utilized in connection with conventional receptacles having standard lids.